A service invoice is a document that outlines the services provided to a customer and the cost associated with those services. It serves as a record of an agreement between two parties, outlining when payment is due and how it should be made. A service invoice is a way for businesses to keep track of time and materials expended in providing services, ensuring that all charges are accounted for and that customers are billed accurately. As such, a service invoice serves a key role in maintaining a strong relationship between business and client.